This invention relates to a method and apparatus for correcting the reciprocity law failure of a photosensitive material, for use in a picture reproducing machine such as a process camera, and the like.
As is well-known, a sensitivity of a color photosensitive material is depressed due to its reciprocity law failure when the illuminance is low. Hence, in order to perform a proper exposure, the exposure time should be corrected. Further, the reciprocity law failures of the three color layers of the photosensitive material are varied depending on the luminous energy, and accordingly the color balance is deteriorated. Therefore, for example, the exposure time for a cyan filter is reduced and the exposure time for a yellow filter is increased.
Meanwhile, even when the exposure is properly performed depending on the average luminous energy by using an ideal photosensitive material whose reciprocity law holds good, or the above described correction of the reciprocity law failure is carried out during the exposure which is performed depending on the average luminous energy by using a usual photosensitive material, a density failure and a color failure occur as follows.
That is, when the dark background of the picture is large, the essential part having a small light area is exposed excessively, and, on the other hand, when the light background is large, the essential part having a small dark area is exposed insufficiently. When the red, green or yellow background of the picture is large, the red, green or yellow color is emphasized in a small essential part.
Heretofore, various methods for correcting such density and color failures have been developed. However, the corrections of the reciprocity law failures against the luminous energy and the color layers of the photosensitive material have been carried out depending on the experiences of a skilled person.